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                                <h1 id="django&#x5165;&#x95E8;&#x4E0E;&#x5B9E;&#x8DF5;-&#x7B2C;20&#x7AE0;&#xFF1A;querysets&#xFF08;&#x67E5;&#x8BE2;&#x7ED3;&#x679C;&#x96C6;&#xFF09;">Django&#x5165;&#x95E8;&#x4E0E;&#x5B9E;&#x8DF5;-&#x7B2C;20&#x7AE0;&#xFF1A;QuerySets&#xFF08;&#x67E5;&#x8BE2;&#x7ED3;&#x679C;&#x96C6;&#xFF09;</h1>
<p>&#x73B0;&#x5728;&#x6211;&#x4EEC;&#x82B1;&#x70B9;&#x65F6;&#x95F4;&#x6765;&#x63A2;&#x7D22;&#x5173;&#x4E8E;&#x6A21;&#x578B;&#x7684; API&#x3002;&#x9996;&#x5148;&#xFF0C;&#x6211;&#x4EEC;&#x6765;&#x6539;&#x8FDB;&#x4E3B;&#x9875;&#xFF1A;</p>
<p><img src="statics/5-13.png" alt="5-13.png"></p>
<p>&#x6709;3&#x4E2A;&#x4EFB;&#x52A1;&#xFF1A;</p>
<ul>
<li>&#x663E;&#x793A;&#x6BCF;&#x4E2A;&#x677F;&#x5757;&#x7684;&#x603B;&#x4E3B;&#x9898;&#x6570;</li>
<li>&#x663E;&#x793A;&#x6BCF;&#x4E2A;&#x677F;&#x5757;&#x7684;&#x603B;&#x56DE;&#x590D;&#x6570;</li>
<li>&#x663E;&#x793A;&#x6BCF;&#x4E2A;&#x677F;&#x5757;&#x7684;&#x6700;&#x540E;&#x53D1;&#x5E03;&#x8005;&#x548C;&#x65E5;&#x671F;</li>
</ul>
<p>&#x5728;&#x5B9E;&#x73B0;&#x8FD9;&#x4E9B;&#x529F;&#x80FD;&#x524D;&#xFF0C;&#x6211;&#x4EEC;&#x5148;&#x4F7F;&#x7528;Python&#x7EC8;&#x7AEF;</p>
<p>&#x56E0;&#x4E3A;&#x6211;&#x4EEC;&#x8981;&#x5728;Python&#x7EC8;&#x7AEF;&#x5C1D;&#x8BD5;&#xFF0C;&#x6240;&#x4EE5;&#xFF0C;&#x628A;&#x6240;&#x6709;&#x7684; models &#x5B9A;&#x4E49;&#x4E00;&#x4E2A; <code>__str__</code> &#x65B9;&#x6CD5;&#x662F;&#x4E2A;&#x597D;&#x4E3B;&#x610F;</p>
<p><strong>boards/models.py</strong>(<a href="https://gist.github.com/vitorfs/9524eb42005697fbb79836285b50b1f4" target="_blank">&#x5B8C;&#x6574;&#x4EE3;&#x7801;</a>)</p>
<pre><code class="lang-python"><span class="hljs-keyword">from</span> django.db <span class="hljs-keyword">import</span> models
<span class="hljs-keyword">from</span> django.utils.text <span class="hljs-keyword">import</span> Truncator

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Board</span><span class="hljs-params">(models.Model)</span>:</span>
    <span class="hljs-comment"># ...</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__str__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> self.name

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Topic</span><span class="hljs-params">(models.Model)</span>:</span>
    <span class="hljs-comment"># ...</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__str__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> self.subject

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Post</span><span class="hljs-params">(models.Model)</span>:</span>
    <span class="hljs-comment"># ...</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__str__</span><span class="hljs-params">(self)</span>:</span>
        truncated_message = Truncator(self.message)
        <span class="hljs-keyword">return</span> truncated_message.chars(<span class="hljs-number">30</span>)
</code></pre>
<p>&#x5728; Post &#x6A21;&#x578B;&#x4E2D;&#xFF0C;&#x4F7F;&#x7528;&#x4E86; <code>Truncator</code> &#x5DE5;&#x5177;&#x7C7B;&#xFF0C;&#x8FD9;&#x662F;&#x5C06;&#x4E00;&#x4E2A;&#x957F;&#x5B57;&#x7B26;&#x4E32;&#x622A;&#x53D6;&#x4E3A;&#x4EFB;&#x610F;&#x957F;&#x5EA6;&#x5B57;&#x7B26;&#x7684;&#x7B80;&#x4FBF;&#x65B9;&#x6CD5;&#xFF08;&#x8FD9;&#x91CC;&#x6211;&#x4EEC;&#x4F7F;&#x7528;30&#x4E2A;&#x5B57;&#x7B26;&#xFF09;</p>
<p>&#x73B0;&#x5728;&#x6253;&#x5F00; Python shell </p>
<pre><code class="lang-shell">python manage.py shell
from boards.models import Board

# First get a board instance from the database
board = Board.objects.get(name=&apos;Django&apos;)
</code></pre>
<p>&#x8FD9;&#x4E09;&#x4E2A;&#x4EFB;&#x52A1;&#x4E2D;&#x6700;&#x7B80;&#x5355;&#x7684;&#x4E00;&#x4E2A;&#x5C31;&#x662F;&#x83B7;&#x53D6;&#x5F53;&#x524D;&#x7248;&#x5757;&#x7684;&#x603B;&#x4E3B;&#x9898;&#x6570;&#xFF0C;&#x56E0;&#x4E3A; Topic &#x548C; Baoard &#x662F;&#x76F4;&#x63A5;&#x5173;&#x8054;&#x7684;&#x3002;</p>
<pre><code class="lang-shell">board.topics.all()
&lt;QuerySet [&lt;Topic: Hello everyone!&gt;, &lt;Topic: Test&gt;, &lt;Topic: Testing a new post&gt;, &lt;Topic: Hi&gt;]&gt;

board.topics.count()
4
</code></pre>
<p>&#x5C31;&#x8FD9;&#x6837;&#x5B50;&#x3002;</p>
<p>&#x73B0;&#x5728;&#x7EDF;&#x8BA1;&#x4E00;&#x4E2A;&#x7248;&#x5757;&#x4E0B;&#x9762;&#x7684;&#x56DE;&#x590D;&#x6570;&#x91CF;&#x6709;&#x70B9;&#x9EBB;&#x70E6;&#xFF0C;&#x56E0;&#x4E3A;&#x56DE;&#x590D;&#x5E76;&#x6CA1;&#x6709;&#x548C; Board &#x76F4;&#x63A5;&#x5173;&#x8054;</p>
<pre><code class="lang-shell">from boards.models import Post

Post.objects.all()
&lt;QuerySet [&lt;Post: This is my first topic.. :-)&gt;, &lt;Post: test.&gt;, &lt;Post: Hi everyone!&gt;,
  &lt;Post: New test here!&gt;, &lt;Post: Testing the new reply feature!&gt;, &lt;Post: Lorem ipsum dolor sit amet,...&gt;,
  &lt;Post: hi there&gt;, &lt;Post: test&gt;, &lt;Post: Testing..&gt;, &lt;Post: some reply&gt;, &lt;Post: Random random.&gt;
]&gt;

Post.objects.count()
11
</code></pre>
<p>&#x8FD9;&#x91CC;&#x4E00;&#x5171;11&#x4E2A;&#x56DE;&#x590D;&#xFF0C;&#x4F46;&#x662F;&#x5B83;&#x5E76;&#x4E0D;&#x5168;&#x90E8;&#x5C5E;&#x4E8E; &quot;Django&quot; &#x8FD9;&#x4E2A;&#x7248;&#x5757;&#x7684;&#x3002;</p>
<p>&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x8FD9;&#x6837;&#x6765;&#x8FC7;&#x6EE4;</p>
<pre><code class="lang-shell">from boards.models import Board, Post

board = Board.objects.get(name=&apos;Django&apos;)

Post.objects.filter(topic__board=board)
&lt;QuerySet [&lt;Post: This is my first topic.. :-)&gt;, &lt;Post: test.&gt;, &lt;Post: hi there&gt;,
  &lt;Post: Hi everyone!&gt;, &lt;Post: Lorem ipsum dolor sit amet,...&gt;, &lt;Post: New test here!&gt;,
  &lt;Post: Testing the new reply feature!&gt;
]&gt;

Post.objects.filter(topic__board=board).count()
7
</code></pre>
<p>&#x53CC;&#x4E0B;&#x5212;&#x7EBF;&#x7684;<code>topic__board</code>&#x7528;&#x4E8E;&#x901A;&#x8FC7;&#x6A21;&#x578B;&#x5173;&#x7CFB;&#x6765;&#x5B9A;&#x4F4D;&#xFF0C;&#x5728;&#x5185;&#x90E8;&#xFF0C;Django &#x5728; Board-Topic-Post&#x4E4B;&#x95F4;&#x6784;&#x5EFA;&#x4E86;&#x6865;&#x6881;&#xFF0C;&#x6784;&#x5EFA;SQL&#x67E5;&#x8BE2;&#x6765;&#x83B7;&#x53D6;&#x5C5E;&#x4E8E;&#x6307;&#x5B9A;&#x7248;&#x5757;&#x4E0B;&#x9762;&#x7684;&#x5E16;&#x5B50;&#x56DE;&#x590D;&#x3002;</p>
<p>&#x6700;&#x540E;&#x4E00;&#x4E2A;&#x4EFB;&#x52A1;&#x662F;&#x6807;&#x8BC6;&#x7248;&#x5757;&#x4E0B;&#x9762;&#x7684;&#x6700;&#x540E;&#x4E00;&#x6761;&#x56DE;&#x590D;</p>
<pre><code class="lang-shell"># order by the `created_at` field, getting the most recent first
Post.objects.filter(topic__board=board).order_by(&apos;-created_at&apos;)
&lt;QuerySet [&lt;Post: testing&gt;, &lt;Post: new post&gt;, &lt;Post: hi there&gt;, &lt;Post: Lorem ipsum dolor sit amet,...&gt;,
  &lt;Post: Testing the new reply feature!&gt;, &lt;Post: New test here!&gt;, &lt;Post: Hi everyone!&gt;,
  &lt;Post: test.&gt;, &lt;Post: This is my first topic.. :-)&gt;
]&gt;

# we can use the `first()` method to just grab the result that interest us
Post.objects.filter(topic__board=board).order_by(&apos;-created_at&apos;).first()
&lt;Post: testing&gt;
</code></pre>
<p>&#x592A;&#x68D2;&#x4E86;&#xFF0C;&#x73B0;&#x5728;&#x6211;&#x4EEC;&#x6765;&#x5B9E;&#x73B0;&#x5B83;</p>
<p><strong>boards/models.py</strong> (<a href="https://gist.github.com/vitorfs/74077336decd75292082752eb8405ad3" target="_blank">&#x5B8C;&#x6574;&#x4EE3;&#x7801;</a>)</p>
<pre><code class="lang-python"><span class="hljs-keyword">from</span> django.db <span class="hljs-keyword">import</span> models

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Board</span><span class="hljs-params">(models.Model)</span>:</span>
    name = models.CharField(max_length=<span class="hljs-number">30</span>, unique=<span class="hljs-keyword">True</span>)
    description = models.CharField(max_length=<span class="hljs-number">100</span>)

    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__str__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> self.name

    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_posts_count</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> Post.objects.filter(topic__board=self).count()

    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_last_post</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> Post.objects.filter(topic__board=self).order_by(<span class="hljs-string">&apos;-created_at&apos;</span>).first()
</code></pre>
<p>&#x6CE8;&#x610F;&#xFF0C;&#x6211;&#x4EEC;&#x4F7F;&#x7528;&#x7684;&#x662F;<code>self</code>&#xFF0C;&#x56E0;&#x4E3A;&#x8FD9;&#x662F;Board&#x7684;&#x4E00;&#x4E2A;&#x5B9E;&#x4F8B;&#x65B9;&#x6CD5;&#xFF0C;&#x6240;&#x4EE5;&#x6211;&#x4EEC;&#x5C31;&#x7528;&#x8FD9;&#x4E2A;Board&#x5B9E;&#x4F8B;&#x6765;&#x8FC7;&#x6EE4;&#x8FD9;&#x4E2A; QuerySet</p>
<p>&#x73B0;&#x5728;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x6539;&#x8FDB;&#x4E3B;&#x9875;&#x7684;HTML&#x6A21;&#x677F;&#x6765;&#x663E;&#x793A;&#x8FD9;&#x4E9B;&#x65B0;&#x7684;&#x4FE1;&#x606F;</p>
<p><strong>templates/home.html</strong></p>
<pre><code class="lang-html">
{% extends &apos;base.html&apos; %}

{% block breadcrumb %}
  <span class="hljs-tag">&lt;<span class="hljs-name">li</span> <span class="hljs-attr">class</span>=<span class="hljs-string">&quot;breadcrumb-item active&quot;</span>&gt;</span>Boards<span class="hljs-tag">&lt;/<span class="hljs-name">li</span>&gt;</span>
{% endblock %}

{% block content %}
  <span class="hljs-tag">&lt;<span class="hljs-name">table</span> <span class="hljs-attr">class</span>=<span class="hljs-string">&quot;table&quot;</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">thead</span> <span class="hljs-attr">class</span>=<span class="hljs-string">&quot;thead-inverse&quot;</span>&gt;</span>
      <span class="hljs-tag">&lt;<span class="hljs-name">tr</span>&gt;</span>
        <span class="hljs-tag">&lt;<span class="hljs-name">th</span>&gt;</span>Board<span class="hljs-tag">&lt;/<span class="hljs-name">th</span>&gt;</span>
        <span class="hljs-tag">&lt;<span class="hljs-name">th</span>&gt;</span>Posts<span class="hljs-tag">&lt;/<span class="hljs-name">th</span>&gt;</span>
        <span class="hljs-tag">&lt;<span class="hljs-name">th</span>&gt;</span>Topics<span class="hljs-tag">&lt;/<span class="hljs-name">th</span>&gt;</span>
        <span class="hljs-tag">&lt;<span class="hljs-name">th</span>&gt;</span>Last Post<span class="hljs-tag">&lt;/<span class="hljs-name">th</span>&gt;</span>
      <span class="hljs-tag">&lt;/<span class="hljs-name">tr</span>&gt;</span>
    <span class="hljs-tag">&lt;/<span class="hljs-name">thead</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">tbody</span>&gt;</span>
      {% for board in boards %}
        <span class="hljs-tag">&lt;<span class="hljs-name">tr</span>&gt;</span>
          <span class="hljs-tag">&lt;<span class="hljs-name">td</span>&gt;</span>
            <span class="hljs-tag">&lt;<span class="hljs-name">a</span> <span class="hljs-attr">href</span>=<span class="hljs-string">&quot;{% url &apos;board_topics&apos; board.pk %}&quot;</span>&gt;</span>{{ board.name }}<span class="hljs-tag">&lt;/<span class="hljs-name">a</span>&gt;</span>
            <span class="hljs-tag">&lt;<span class="hljs-name">small</span> <span class="hljs-attr">class</span>=<span class="hljs-string">&quot;text-muted d-block&quot;</span>&gt;</span>{{ board.description }}<span class="hljs-tag">&lt;/<span class="hljs-name">small</span>&gt;</span>
          <span class="hljs-tag">&lt;/<span class="hljs-name">td</span>&gt;</span>
          <span class="hljs-tag">&lt;<span class="hljs-name">td</span> <span class="hljs-attr">class</span>=<span class="hljs-string">&quot;align-middle&quot;</span>&gt;</span>
            {{ board.get_posts_count }}
          <span class="hljs-tag">&lt;/<span class="hljs-name">td</span>&gt;</span>
          <span class="hljs-tag">&lt;<span class="hljs-name">td</span> <span class="hljs-attr">class</span>=<span class="hljs-string">&quot;align-middle&quot;</span>&gt;</span>
            {{ board.topics.count }}
          <span class="hljs-tag">&lt;/<span class="hljs-name">td</span>&gt;</span>
          <span class="hljs-tag">&lt;<span class="hljs-name">td</span> <span class="hljs-attr">class</span>=<span class="hljs-string">&quot;align-middle&quot;</span>&gt;</span>
            {% with post=board.get_last_post %}
              <span class="hljs-tag">&lt;<span class="hljs-name">small</span>&gt;</span>
                <span class="hljs-tag">&lt;<span class="hljs-name">a</span> <span class="hljs-attr">href</span>=<span class="hljs-string">&quot;{% url &apos;topic_posts&apos; board.pk post.topic.pk %}&quot;</span>&gt;</span>
                  By {{ post.created_by.username }} at {{ post.created_at }}
                <span class="hljs-tag">&lt;/<span class="hljs-name">a</span>&gt;</span>
              <span class="hljs-tag">&lt;/<span class="hljs-name">small</span>&gt;</span>
            {% endwith %}
          <span class="hljs-tag">&lt;/<span class="hljs-name">td</span>&gt;</span>
        <span class="hljs-tag">&lt;/<span class="hljs-name">tr</span>&gt;</span>
      {% endfor %}
    <span class="hljs-tag">&lt;/<span class="hljs-name">tbody</span>&gt;</span>
  <span class="hljs-tag">&lt;/<span class="hljs-name">table</span>&gt;</span>
{% endblock %}
</code></pre>
<p>&#x73B0;&#x5728;&#x662F;&#x8FD9;&#x6837;&#x7684;&#x6548;&#x679C;</p>
<p><img src="statics/5-14.png" alt="5-14.png"></p>
<p>&#x8FD0;&#x884C;&#x6D4B;&#x8BD5;&#xFF1A;</p>
<pre><code class="lang-shell">python manage.py test
</code></pre>
<pre><code class="lang-shell">Creating test database for alias &apos;default&apos;...
System check identified no issues (0 silenced).
.......................................................EEE......................
======================================================================
ERROR: test_home_url_resolves_home_view (boards.tests.test_view_home.HomeTests)
----------------------------------------------------------------------
django.urls.exceptions.NoReverseMatch: Reverse for &apos;topic_posts&apos; with arguments &apos;(1, &apos;&apos;)&apos; not found. 1 pattern(s) tried: [&apos;boards/(?P&lt;pk&gt;\\d+)/topics/(?P&lt;topic_pk&gt;\\d+)/$&apos;]

======================================================================
ERROR: test_home_view_contains_link_to_topics_page (boards.tests.test_view_home.HomeTests)
----------------------------------------------------------------------
django.urls.exceptions.NoReverseMatch: Reverse for &apos;topic_posts&apos; with arguments &apos;(1, &apos;&apos;)&apos; not found. 1 pattern(s) tried: [&apos;boards/(?P&lt;pk&gt;\\d+)/topics/(?P&lt;topic_pk&gt;\\d+)/$&apos;]

======================================================================
ERROR: test_home_view_status_code (boards.tests.test_view_home.HomeTests)
----------------------------------------------------------------------
django.urls.exceptions.NoReverseMatch: Reverse for &apos;topic_posts&apos; with arguments &apos;(1, &apos;&apos;)&apos; not found. 1 pattern(s) tried: [&apos;boards/(?P&lt;pk&gt;\\d+)/topics/(?P&lt;topic_pk&gt;\\d+)/$&apos;]

----------------------------------------------------------------------
Ran 80 tests in 5.663s

FAILED (errors=3)
Destroying test database for alias &apos;default&apos;...
</code></pre>
<p>&#x770B;&#x8D77;&#x6765;&#x597D;&#x50CF;&#x6709;&#x95EE;&#x9898;&#xFF0C;&#x5982;&#x679C;&#x6CA1;&#x6709;&#x56DE;&#x590D;&#x7684;&#x65F6;&#x5019;&#x7A0B;&#x5E8F;&#x4F1A;&#x5D29;&#x6E83;</p>
<p><strong>templates/home.html</strong></p>
<pre><code class="lang-python">{% with post=board.get_last_post %}
  {% if post %}
    &lt;small&gt;
      &lt;a href=&quot;{% url &apos;topic_posts&apos; board.pk post.topic.pk %}&quot;&gt;
        By {{ post.created_by.username }} at {{ post.created_at }}
      &lt;/a&gt;
    &lt;/small&gt;
  {% else %}
    &lt;small class=&quot;text-muted&quot;&gt;
      &lt;em&gt;No posts yet.&lt;/em&gt;
    &lt;/small&gt;
  {% endif %}
{% endwith %}
</code></pre>
<p>&#x518D;&#x6B21;&#x8FD0;&#x884C;&#x6D4B;&#x8BD5;&#xFF1A;</p>
<pre><code class="lang-shell">python manage.py test
</code></pre>
<pre><code class="lang-shell">Creating test database for alias &apos;default&apos;...
System check identified no issues (0 silenced).
................................................................................
----------------------------------------------------------------------
Ran 80 tests in 5.630s

OK
Destroying test database for alias &apos;default&apos;...
</code></pre>
<p>&#x6211;&#x6DFB;&#x52A0;&#x4E00;&#x4E2A;&#x6CA1;&#x6709;&#x4EFB;&#x4F55;&#x6D88;&#x606F;&#x7684;&#x7248;&#x5757;&#xFF0C;&#x7528;&#x4E8E;&#x68C0;&#x67E5;&#x8FD9;&#x4E2A;&quot;&#x7A7A;&#x6D88;&#x606F;&quot;</p>
<p><img src="statics/5-15.png" alt="5-15.png"></p>
<p>&#x73B0;&#x5728;&#x662F;&#x65F6;&#x5019;&#x6765;&#x6539;&#x8FDB;&#x56DE;&#x590D;&#x5217;&#x8868;&#x9875;&#x9762;&#x4E86;&#x3002;</p>
<p><img src="statics/5-16.png" alt="5-16.png"></p>
<p>&#x73B0;&#x5728;&#xFF0C;&#x6211;&#x5C06;&#x544A;&#x8BC9;&#x4F60;&#x53E6;&#x5916;&#x4E00;&#x79CD;&#x65B9;&#x6CD5;&#x6765;&#x7EDF;&#x8BA1;&#x56DE;&#x590D;&#x7684;&#x6570;&#x91CF;&#xFF0C;&#x7528;&#x4E00;&#x79CD;&#x66F4;&#x9AD8;&#x6548;&#x7684;&#x65B9;&#x5F0F;</p>
<p>&#x548C;&#x4E4B;&#x524D;&#x4E00;&#x6837;&#xFF0C;&#x9996;&#x5148;&#x5728;Python shell &#x4E2D;&#x5C1D;&#x8BD5;</p>
<pre><code class="lang-shell">python manage.py shell
</code></pre>
<pre><code class="lang-python"><span class="hljs-keyword">from</span> django.db.models <span class="hljs-keyword">import</span> Count
<span class="hljs-keyword">from</span> boards.models <span class="hljs-keyword">import</span> Board

board = Board.objects.get(name=<span class="hljs-string">&apos;Django&apos;</span>)

topics = board.topics.order_by(<span class="hljs-string">&apos;-last_updated&apos;</span>).annotate(replies=Count(<span class="hljs-string">&apos;posts&apos;</span>))

<span class="hljs-keyword">for</span> topic <span class="hljs-keyword">in</span> topics:
    print(topic.replies)

<span class="hljs-number">2</span>
<span class="hljs-number">4</span>
<span class="hljs-number">2</span>
<span class="hljs-number">1</span>
</code></pre>
<p>&#x8FD9;&#x91CC;&#x6211;&#x4EEC;&#x4F7F;&#x7528;<code>annotate</code> &#xFF0C;QuerySet&#x5C06;&#x5373;&#x65F6;&#x751F;&#x6210;&#x4E00;&#x4E2A;&#x65B0;&#x7684;&#x5217;&#xFF0C;&#x8FD9;&#x4E2A;&#x65B0;&#x7684;&#x5217;&#xFF0C;&#x5C06;&#x88AB;&#x7FFB;&#x8BD1;&#x6210;&#x4E00;&#x4E2A;&#x5C5E;&#x6027;&#xFF0C;&#x53EF;&#x901A;&#x8FC7; <code>topic.replies</code>&#x6765;&#x8BBF;&#x95EE;&#xFF0C;&#x5B83;&#x5305;&#x542B;&#x4E86;&#x6307;&#x5B9A;&#x4E3B;&#x9898;&#x4E0B;&#x7684;&#x56DE;&#x590D;&#x6570;&#x3002;</p>
<p>&#x6211;&#x4EEC;&#x6765;&#x505A;&#x4E00;&#x4E2A;&#x5C0F;&#x5C0F;&#x7684;&#x4FEE;&#x590D;&#xFF0C;&#x56E0;&#x4E3A;&#x56DE;&#x590D;&#x91CC;&#x9762;&#x4E0D;&#x5E94;&#x8BE5;&#x5305;&#x62EC;&#x53D1;&#x8D77;&#x8005;&#x7684;&#x5E16;&#x5B50;</p>
<pre><code class="lang-python">topics = board.topics.order_by(<span class="hljs-string">&apos;-last_updated&apos;</span>).annotate(replies=Count(<span class="hljs-string">&apos;posts&apos;</span>) - <span class="hljs-number">1</span>)

<span class="hljs-keyword">for</span> topic <span class="hljs-keyword">in</span> topics:
    print(topic.replies)

<span class="hljs-number">1</span>
<span class="hljs-number">3</span>
<span class="hljs-number">1</span>
<span class="hljs-number">0</span>
</code></pre>
<p>&#x5F88;&#x9177;&#xFF0C;&#x5BF9;&#x4E0D;&#x5BF9;&#xFF1F;</p>
<p><strong>boards/views.py</strong> (<a href="https://gist.github.com/vitorfs/f22b493b3e076aba9351c9d98f547f5e#file-views-py-L14" target="_blank">&#x5B8C;&#x6574;&#x4EE3;&#x7801;</a>)</p>
<pre><code class="lang-python"><span class="hljs-keyword">from</span> django.db.models <span class="hljs-keyword">import</span> Count
<span class="hljs-keyword">from</span> django.shortcuts <span class="hljs-keyword">import</span> get_object_or_404, render
<span class="hljs-keyword">from</span> .models <span class="hljs-keyword">import</span> Board

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">board_topics</span><span class="hljs-params">(request, pk)</span>:</span>
    board = get_object_or_404(Board, pk=pk)
    topics = board.topics.order_by(<span class="hljs-string">&apos;-last_updated&apos;</span>).annotate(replies=Count(<span class="hljs-string">&apos;posts&apos;</span>) - <span class="hljs-number">1</span>)
    <span class="hljs-keyword">return</span> render(request, <span class="hljs-string">&apos;topics.html&apos;</span>, {<span class="hljs-string">&apos;board&apos;</span>: board, <span class="hljs-string">&apos;topics&apos;</span>: topics})
</code></pre>
<p><strong>templates/topics.html</strong>(<a href="https://gist.github.com/vitorfs/1a2235f05f436c92025dc86028c22fc4#file-topics-html-L28" target="_blank">&#x5B8C;&#x6574;&#x4EE3;&#x7801;</a>)</p>
<pre><code class="lang-html">
{% for topic in topics %}
  <span class="hljs-tag">&lt;<span class="hljs-name">tr</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">td</span>&gt;</span><span class="hljs-tag">&lt;<span class="hljs-name">a</span> <span class="hljs-attr">href</span>=<span class="hljs-string">&quot;{% url &apos;topic_posts&apos; board.pk topic.pk %}&quot;</span>&gt;</span>{{ topic.subject }}<span class="hljs-tag">&lt;/<span class="hljs-name">a</span>&gt;</span><span class="hljs-tag">&lt;/<span class="hljs-name">td</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">td</span>&gt;</span>{{ topic.starter.username }}<span class="hljs-tag">&lt;/<span class="hljs-name">td</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">td</span>&gt;</span>{{ topic.replies }}<span class="hljs-tag">&lt;/<span class="hljs-name">td</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">td</span>&gt;</span>0<span class="hljs-tag">&lt;/<span class="hljs-name">td</span>&gt;</span>
    <span class="hljs-tag">&lt;<span class="hljs-name">td</span>&gt;</span>{{ topic.last_updated }}<span class="hljs-tag">&lt;/<span class="hljs-name">td</span>&gt;</span>
  <span class="hljs-tag">&lt;/<span class="hljs-name">tr</span>&gt;</span>
{% endfor %}
</code></pre>
<p><img src="statics/topics-5-15.png" alt="topics-5-15.png"></p>
<p>&#x4E0B;&#x4E00;&#x6B65;&#x662F;&#x4FEE;&#x590D;&#x4E3B;&#x9898;&#x7684;&#x67E5;&#x770B;&#x6B21;&#x6570;&#xFF0C;&#x4F46;&#x662F;&#xFF0C;&#x73B0;&#x5728;&#x6211;&#x4EEC;&#x9700;&#x8981;&#x6DFB;&#x52A0;&#x4E00;&#x4E2A;&#x65B0;&#x7684;&#x5B57;&#x6BB5;</p>

                                
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